Metal-Supported Aluminosilicate Ultrathin Films as a Versatile Tool for Studying the Surface Chemistry of Zeolites

Two-Dimensional Ultrathin Silica Films

Two-dimensional (2D) ultrathin silica films have the potential to reach technological importance in electronics and catalysis. Several well-defined 2D-silica structures have been synthesized so far. The silica bilayer represents a 2D material with SiO₂ stoichiometry. It consists of precisely two layers of tetrahedral [SiO₄] building blocks, corner connected via oxygen bridges, thus forming a self-saturated silicon dioxide sheet with a thickness of ∼0.5 nm. Inspired by recent successful preparations and characterizations of these 2D-silica model systems, scientists now can forge novel concepts for realistic systems, particularly by atomic-scale studies with the most powerful and advanced surface science techniques and density functional theory calculations. This Review provides a solid introduction to these recent developments, breakthroughs, and implications on ultrathin 2D-silica films, including their atomic/electronic structures, chemical modifications, atom/molecule adsorptions, and catalytic reactivity properties, which can help to stimulate further investigations and understandings of these fundamentally important 2D materials.

Persistent homology in two-dimensional atomic networks

The topology of two-dimensional network materials is investigated by persistent homology analysis. The constraint of two dimensions allows for a direct comparison of key persistent homology metrics (persistence diagrams, cycles, and Betti numbers) with more traditional metrics such as the ring-size distributions. Two different types of networks are employed in which the topology is manipulated systematically. In the first, comparatively rigid networks are generated for a triangle-raft model, which are representative of materials such as silica bilayers. In the second, more flexible networks are generated using a bond-switching algorithm, which are representative of materials such as graphene. Bands are identified in the persistence diagrams by reference to the length scales associated with distorted polygons. The triangle-raft models with the largest ordering allow specific bands B_n (n = 1, 2, 3, …) to be allocated to configurations of atoms separated by n bonds. The persistence diagrams for the more disordered network models also display bands albeit less pronounced. The persistent homology method thereby provides information on n-body correlations that is not accessible from structure factors or radial distribution functions. An analysis of the persistent cycles gives the primitive ring statistics, provided the level of disorder is not too large. The method also gives information on the regularity of rings that is unavailable from a ring-statistics analysis. The utility of the persistent homology method is demonstrated by its application to experimentally-obtained configurations of silica bilayers and graphene.

Ring structure of selected two-dimensional procrystalline lattices

Recent work has introduced the term "procrystalline" to define systems which lack translational symmetry but have an underlying high-symmetry lattice. The properties of five such two-dimensional (2D) lattices are considered in terms of the topologies of rings which may be formed from three-coordinate sites only. Parent lattices with full coordination numbers of four, five, and six are considered, with configurations generated using a Monte Carlo algorithm. The different lattices are shown to generate configurations with varied ring distributions. The different constraints imposed by the underlying lattices are discussed. Ring size distributions are obtained analytically for two of the simpler lattices considered (the square and trihexagonal nets). In all cases, the ring size distributions are compared to those obtained via a maximum entropy method. The configurations are analyzed with respect to the near-universal Lemaître curve (which connects the fraction of six-membered rings with the width of the ring size distribution) and three lattices are highlighted as rare examples of systems which generate configurations which do not map onto this curve. The assortativities are considered, which contain information on the degree of ordering of different sized rings within a given distribution. All of the systems studied show systematically greater assortativities when compared to those generated using a standard bond-switching method. Comparison is also made to two series of crystalline motifs which shown distinctive behavior in terms of both the ring size distributions and the assortativities. Procrystalline lattices are therefore shown to have fundamentally different behavior to traditional disordered and crystalline systems, indicative of the partial ordering of the underlying lattices.

Characterization of certain Nigerian clay minerals for water purification and other industrial applications

Seven Nigerian clays and clay minerals were characterized by multiple means with respect to their potential application in water purification and other industrial areas. The morphology was determined by means of SEM while chemical/mineral compositions were quantified using EDX, XPS and XRD. FT-IR and UV methods were employed to investigate the functional groups, inter alia the physical and chemical behaviours of adsorbed species. The stability in aqueous solution was determined by zeta potential measurements. The combined results revealed that the clays are mostly kaolin and illite, while clay minerals are predominantly gibbsite and quartz, although other clay-associated minerals and elements were also observed. Two out of the characterized samples will find suitable application in filter media production for water purification due to the possession of exchangeable cations and electrophoresis properties, while the others possess potential industrial applications for refractory linings, ceramics, medical, beauty and cosmetics products. This outcome implies a utilization increase in local content and a value addition to minerals in Nigeria. The results of the study are being used to design and facilitate expanded clay aggregate production to be used for the development of low-cost water filters to address the challenge of poor access to potable water in Africa and other developing continents.

Catalytic role of solid acid catalysts in glycerol acetylation for the production of bio-additives: a review

The influencing factors of Brønsted acid and Lewis acid in glycerol acetylation to potential bioadditives (mono-, di- and triacetin) are detailed. The important catalytic role and operating conditions toward conversion and selectivity are suggested.

Preparation and structure of Fe-containing aluminosilicate thin films

Fe-containing aluminosilicate thin films exhibit a phase separation, which makes the formation of in-frame Fe in aluminosilicates (zeolites) unfavourable.

Ultra-thin silicate films on metals

Silica is one of the key materials in many modern technological applications. 'Surface science' approach for understanding surface chemistry on silica-based materials, on the one hand, and further miniaturization of new generation electronic devices, on the other, all these face the necessity of rational design of the ultrathin silica films on electrically conductive substrates. The review updates recent studies in this field. Despite the structural complexity and diversity of silica, substantial progress has recently been achieved in understanding of the atomic structure of truly 2D silicates.